shared: add nm-secret-utils.h helper

We already had nm_free_secret() to clear the secret out
of a NUL terminated string. That works well for secrets
which are strings, it can be used with a cleanup attribute
(nm_auto_free_secret) and as a cleanup function for a
GBytes.

However, it does not work for secrets which are binary.
For those, we must also track the length of the allocated
data and clear it.

Add two new structs NMSecretPtr and NMSecretBuf to help
with that.

Makefile.am

@@ -501,6 +501,7 @@ libnm_core_lib_h_priv = \
 	shared/nm-utils/nm-dedup-multi.h \
 	shared/nm-utils/nm-enum-utils.h \
 	shared/nm-utils/nm-hash-utils.h \
+	shared/nm-utils/nm-secret-utils.h \
 	shared/nm-utils/nm-shared-utils.h \
 	shared/nm-utils/nm-random-utils.h \
 	shared/nm-utils/nm-udev-utils.h \
@@ -567,6 +568,7 @@ libnm_core_lib_c_real = \
 	shared/nm-utils/nm-dedup-multi.c \
 	shared/nm-utils/nm-enum-utils.c \
 	shared/nm-utils/nm-hash-utils.c \
+	shared/nm-utils/nm-secret-utils.c \
 	shared/nm-utils/nm-shared-utils.c \
 	shared/nm-utils/nm-random-utils.c \
 	shared/nm-utils/nm-udev-utils.c \
@@ -4736,6 +4738,8 @@ EXTRA_DIST += \
 	shared/nm-utils/nm-jansson.h \
 	shared/nm-utils/nm-obj.h \
 	shared/nm-utils/nm-macros-internal.h \
+	shared/nm-utils/nm-secret-utils.c \
+	shared/nm-utils/nm-secret-utils.h \
 	shared/nm-utils/nm-shared-utils.c \
 	shared/nm-utils/nm-shared-utils.h \
 	shared/nm-utils/nm-test-utils.h \

libnm-core/nm-setting-vpn.c

@@ -25,6 +25,8 @@
 #include <errno.h>
 #include <stdlib.h>
 
+#include "nm-utils/nm-secret-utils.h"
+
 #include "nm-setting-vpn.h"
 #include "nm-utils.h"
 #include "nm-utils-private.h"

libnm/nm-vpn-service-plugin.c

@@ -27,6 +27,7 @@
 #include <signal.h>
 #include <stdlib.h>
 
+#include "nm-utils/nm-secret-utils.h"
 #include "nm-enum-types.h"
 #include "nm-utils.h"
 #include "nm-connection.h"

shared/meson.build

@@ -51,6 +51,7 @@ shared_files_libnm_core = files('''
     nm-utils/nm-enum-utils.c
     nm-utils/nm-hash-utils.c
     nm-utils/nm-random-utils.c
+    nm-utils/nm-secret-utils.c
     nm-utils/nm-shared-utils.c
     nm-utils/nm-udev-utils.c
 '''.split())

shared/nm-utils/nm-macros-internal.h

@@ -207,7 +207,6 @@ NM_AUTO_DEFINE_FCN0 (GKeyFile *, gs_local_keyfile_unref, g_key_file_unref)
 /*****************************************************************************/
 
 static inline int nm_close (int fd);
-static inline void nm_free_secret (char *secret);
 
 /**
  * nm_auto_free:
@@ -238,16 +237,6 @@ NM_AUTO_DEFINE_FCN (GList *, _nm_auto_free_list, g_list_free)
 NM_AUTO_DEFINE_FCN0 (GChecksum *, _nm_auto_checksum_free, g_checksum_free)
 #define nm_auto_free_checksum nm_auto(_nm_auto_checksum_free)
 
-NM_AUTO_DEFINE_FCN (char *, _nm_auto_free_secret, nm_free_secret)
-/**
- * nm_auto_free_secret:
- *
- * Call g_free() on a variable location when it goes out of scope.
- * Also, previously, calls memset(loc, 0, strlen(loc)) to clear out
- * the secret.
- */
-#define nm_auto_free_secret nm_auto(_nm_auto_free_secret)
-
 #define nm_auto_unset_gvalue nm_auto(g_value_unset)
 
 NM_AUTO_DEFINE_FCN_VOID0 (void *, _nm_auto_unref_gtypeclass, g_type_class_unref)
@@ -830,15 +819,6 @@ fcn (void) \
 
 /*****************************************************************************/
 
-static inline void
-nm_free_secret (char *secret)
-{
-	if (secret) {
-		memset (secret, 0, strlen (secret));
-		g_free (secret);
-	}
-}
-
 static inline GString *
 nm_gstring_prepare (GString **l)
 {

shared/nm-utils/nm-secret-utils.c

@@ -0,0 +1,134 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: t; c-basic-offset: 4 -*- */
+/* NetworkManager -- Network link manager
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301 USA.
+ *
+ * (C) Copyright 2018 Red Hat, Inc.
+ */
+
+#include "nm-default.h"
+
+#include "nm-secret-utils.h"
+
+/*****************************************************************************/
+
+void
+nm_explicit_bzero (void *s, gsize n)
+{
+	/* gracefully handle n == 0. This is important, callers rely on it. */
+	if (n > 0) {
+		nm_assert (s);
+#if defined (HAVE_DECL_EXPLICIT_BZERO) && HAVE_DECL_EXPLICIT_BZERO
+		explicit_bzero (s, n);
+#else
+		/* don't bother with a workaround. Use a reasonable glibc. */
+		memset (s, 0, n);
+#endif
+	}
+}
+
+/*****************************************************************************/
+
+char *
+nm_secret_strchomp (char *secret)
+{
+	gsize len;
+
+	g_return_val_if_fail (secret, NULL);
+
+	/* it's actually identical to g_strchomp(). However,
+	 * the glib function does not document, that it clears the
+	 * memory. For @secret, we don't only want to truncate trailing
+	 * spaces, we want to overwrite them with NUL. */
+
+	len = strlen (secret);
+	while (len--) {
+		if (g_ascii_isspace ((guchar) secret[len]))
+			secret[len] = '\0';
+		else
+			break;
+	}
+
+	return secret;
+}
+
+/*****************************************************************************/
+
+GBytes *
+nm_secret_copy_to_gbytes (gconstpointer mem, gsize mem_len)
+{
+	NMSecretBuf *b;
+
+	if (mem_len == 0)
+		return g_bytes_new_static ("", 0);
+
+	nm_assert (mem);
+
+	/* NUL terminate the buffer.
+	 *
+	 * The entire buffer is already malloc'ed and likely has some room for padding.
+	 * Thus, in many situations, this additional byte will cause no overhead in
+	 * practice.
+	 *
+	 * Even if it causes an overhead, do it just for safety. Yes, the returned
+	 * bytes is not a NUL terminated string and no user must rely on this. Do
+	 * not treat binary data as NUL terminated strings, unless you know what
+	 * you are doing. Anyway, defensive FTW.
+	 */
+
+	b = nm_secret_buf_new (mem_len + 1);
+	memcpy (b->bin, mem, mem_len);
+	b->bin[mem_len] = 0;
+	return nm_secret_buf_to_gbytes_take (b, mem_len);
+}
+
+/*****************************************************************************/
+
+NMSecretBuf *
+nm_secret_buf_new (gsize len)
+{
+	NMSecretBuf *secret;
+
+	nm_assert (len > 0);
+
+	secret = g_malloc (sizeof (NMSecretBuf) + len);
+	*((gsize *) &(secret->len)) = len;
+	return secret;
+}
+
+static void
+_secret_buf_free (gpointer user_data)
+{
+	NMSecretBuf *secret = user_data;
+
+	nm_assert (secret);
+	nm_assert (secret->len > 0);
+
+	nm_explicit_bzero (secret->bin, secret->len);
+	g_free (user_data);
+}
+
+GBytes *
+nm_secret_buf_to_gbytes_take (NMSecretBuf *secret, gssize actual_len)
+{
+	nm_assert (secret);
+	nm_assert (secret->len > 0);
+	nm_assert (actual_len == -1 || (actual_len >= 0 && actual_len <= secret->len));
+	return g_bytes_new_with_free_func (secret->bin,
+	                                   actual_len >= 0 ? (gsize) actual_len : secret->len,
+	                                   _secret_buf_free,
+	                                   secret);
+}

shared/nm-utils/nm-secret-utils.h

@@ -0,0 +1,151 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: t; c-basic-offset: 4 -*- */
+/* NetworkManager -- Network link manager
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301 USA.
+ *
+ * (C) Copyright 2018 Red Hat, Inc.
+ */
+
+#ifndef __NM_SECRET_UTILS_H__
+#define __NM_SECRET_UTILS_H__
+
+#include "nm-macros-internal.h"
+
+/*****************************************************************************/
+
+void nm_explicit_bzero (void *s, gsize n);
+
+/*****************************************************************************/
+
+char *nm_secret_strchomp (char *secret);
+
+/*****************************************************************************/
+
+static inline void
+nm_free_secret (char *secret)
+{
+	if (secret) {
+		nm_explicit_bzero (secret, strlen (secret));
+		g_free (secret);
+	}
+}
+
+NM_AUTO_DEFINE_FCN (char *, _nm_auto_free_secret, nm_free_secret)
+/**
+ * nm_auto_free_secret:
+ *
+ * Call g_free() on a variable location when it goes out of scope.
+ * Also, previously, calls memset(loc, 0, strlen(loc)) to clear out
+ * the secret.
+ */
+#define nm_auto_free_secret nm_auto(_nm_auto_free_secret)
+
+/*****************************************************************************/
+
+GBytes *nm_secret_copy_to_gbytes (gconstpointer mem, gsize mem_len);
+
+/*****************************************************************************/
+
+/* NMSecretPtr is a pair of malloc'ed data pointer and the length of the
+ * data. The purpose is to use it in combination with nm_auto_clear_secret_ptr
+ * which ensures that the data pointer (with all len bytes) is cleared upon
+ * cleanup. */
+typedef struct {
+	gsize len;
+
+	/* the data pointer. This pointer must be allocated with malloc (at least
+	 * when used with nm_secret_ptr_clear()). */
+	union {
+		char *str;
+		void *ptr;
+		guint8 *bin;
+	};
+} NMSecretPtr;
+
+static inline void
+nm_secret_ptr_clear (NMSecretPtr *secret)
+{
+	if (secret) {
+		if (secret->len > 0) {
+			if (secret->ptr)
+				nm_explicit_bzero (secret->ptr, secret->len);
+			secret->len = 0;
+		}
+		nm_clear_g_free (&secret->ptr);
+	}
+}
+
+#define nm_auto_clear_secret_ptr nm_auto(nm_secret_ptr_clear)
+
+#define NM_SECRET_PTR_STATIC(_len) \
+	((const NMSecretPtr) { \
+		.len = _len, \
+		.ptr = ((guint8 [_len]) { }), \
+	})
+
+static inline void
+nm_secret_ptr_clear_static (const NMSecretPtr *secret)
+{
+	if (secret) {
+		if (secret->len > 0) {
+			nm_assert (secret->ptr);
+			nm_explicit_bzero (secret->ptr, secret->len);
+		}
+	}
+}
+
+#define nm_auto_clear_static_secret_ptr nm_auto(nm_secret_ptr_clear_static)
+
+static inline void
+nm_secret_ptr_move (NMSecretPtr *dst, NMSecretPtr *src)
+{
+	if (dst && dst != src) {
+		*dst = *src;
+		src->len = 0;
+		src->ptr = NULL;
+	}
+}
+
+/*****************************************************************************/
+
+typedef struct {
+	const gsize len;
+	union {
+		char str[0];
+		guint8 bin[0];
+	};
+} NMSecretBuf;
+
+static inline void
+_nm_auto_free_secret_buf (NMSecretBuf **ptr)
+{
+	NMSecretBuf *b = *ptr;
+
+	if (b) {
+		nm_assert (b->len > 0);
+		nm_explicit_bzero (b->bin, b->len);
+		g_free (b);
+	}
+}
+#define nm_auto_free_secret_buf nm_auto(_nm_auto_free_secret_buf)
+
+NMSecretBuf *nm_secret_buf_new (gsize len);
+
+GBytes *nm_secret_buf_to_gbytes_take (NMSecretBuf *secret, gssize actual_len);
+
+/*****************************************************************************/
+
+#endif /* __NM_SECRET_UTILS_H__ */